The present invention relates to a method and a system for pressurising and dispensing fluid products stored in a bottle, can, container or similar device.
Fluid products such as liquids, pastes, gels, foams and the like are often stored in sealed and pressurized containers such as cans. Such pressurized containers typically have a dispensing device for allowing a controlled dispensing of the fluid product. The dispensing device includes a dispensing valve which is normally in a closed non-dispensing position preventing any fluid product from leaving the container. The dispensing valve may selectively by user interaction be temporarily switched to an open dispensing position allowing the fluid product to advance from an inner space inside the container towards the outside of the container. In some cases the fluid product should be dispensed in an aerosol state or spray state. In such cases the valve may preferably be of the well known “atomizer” type described in e.g. U.S. Pat. No. 1,800,156. Fluid products which are preferably dispensed in the form of an aerosol include hairspray, spray-paint and insect repellent. The pressurized container typically including a propellant gas subjecting the fluid product to a driving pressure for causing the product to flow out of the container through the dispensing device provided the valve is in its open position.
The propellant gas may in some cases be mixed together with the product, which may be particularly advantageous in case the fluid product should be dispensed as a foam, e.g. shaving foam, whipped cream, fire-extinguishing foam and the like. In other cases when the fluid product should be dispensed in the form of a gel or paste, e.g. body lotion, it is desired to separate the propellant gas from the fluid product. The separation may be achieved by a flexible membrane or the like which will allow pressure forces to be communicated between the fluid product and the propellant gas. In some cases the propellant gas is initially held liquefied at high pressure inside the container and vaporizes as the product is being dispensed and the pressure falls. The liquid and gaseous propellant then form an equilibrium for maintaining a constant high driving pressure. In some cases the propellant gas itself constitutes the fluid product, e.g. liquefied petroleum gas, which is stored partially in liquid state and partially in gaseous state.
The inner space of the pressurized container is divided into a pressure space, typically forming a head space of the container and including the propellant gas, and a product space including the fluid product. As the product dispensing is typically performed having the container in an upright position with the fluid product occupying the lower portion of the container and the propellant gas occupying the upper portion of the container, the dispensing device must include an ascending pipe for allowing the fluid product to be dispensed from the bottom of the container and avoiding propellant gas escaping from the pressure space at the top of the container. Alternatively, the pressure space and the product space may be physically separated by a flexible membrane as described above. For economic reasons the pressure space should be as small as possible for allowing small containers to be manufactured having a large amount of useful product.
When the product is being dispensed from the inner space of the container to the outside, the volume of the product space is being reduced. While dispensing, the product space is being substituted by the pressure space which thus will increase in volume. According to the universal gas law the driving pressure, which is the pressure inside the pressure space, will be reduced as the volume of the pressure space increases, provided the amount of gas and the temperature remain constant. For allowing the complete dispensing of the product, a sufficient driving pressure must still remain when the product is completed. The smallest sufficient driving pressure is contemplated to be between 0.1 bar above the atmospheric pressure for a substantially non-viscous product, up to 1 bar or more depending on the properties of the fluid product which is intended to be dispensed. Typically, a high initial pressure of the propellant gas in the pressure space is needed for allowing a sufficiently high pressure to remain in the pressure space for the product to be completely dispensed. Initial driving pressure as high as 6-12 bar and more are commonly used in conventional pressurized cans, such as spray cans, for allowing a driving pressure of about 1 bar to remain after the dispensing of the product has been completed.
The initially high driving pressure will sink significantly when some amount of the product has been dispensed due to the volume increase of the pressure space. A large difference in the driving pressure during the lifetime of the product is undesired, since the initial dose of product will be dispensed at a high driving pressure and the final dose of product will be dispensed at a low driving pressure. The difference in driving pressures between a container being full of product compared to a container where the product is nearly completely dispensed yields an entirely different dispensing behaviour for the initial dose of product and the final dose of product. An unexpectedly high driving pressure may surprise some users and cause an excessive amount product to be dispensed, while a low driving pressure may cause a slow dispensing of the product thereby extending the dispensing time. For some products the successful usage of the product depends entirely on the driving pressure, e.g. sprays and foams typically need a specific driving pressure for a correct spray/foam formation, and the application of the product may be complicated in case the actual driving pressure varies from the specific driving pressure. It is therefore a need for technologies for maintaining a substantially constant dispensing pressure during the complete useful lifetime of the dispenser assembly.
It has been experienced by users that the amount of propellant gas in some cases is insufficient and the driving pressure is below the limit for allowing dispensing before dispensing of the product is completed. The limit for allowing dispensing may be different for different products, but it is contemplated that the driving pressure must remain between 0.1 and 2 bar, typically 0.5 bar, above the atmospheric pressure for overcoming the flow resistance in the dispensing device and achieving a suitable dispensing performance. Normally, the user has no possibility of re-pressurising the pressure space since the container is sealed and cannot be opened without the use of professional tools. In case of insufficient driving pressure, the dispensing operation must be interrupted and the user will typically have to consider the remaining product as being unrecoverable.
There may be several reasons for experiencing insufficient driving pressure in the pressure space, e.g. leakage from the container or improper handling of the container. A well known example of improper handling of the container is in the case of the container having a unitary inner space, i.e. no separation between the pressure space and the product space, to place the container upside down, thereby dispensing from the pressure space instead of from the beverage space. Such a dispensing position may deplete the propellant gas within a short time, rendering the remaining product inaccessible. It is thus an object of the present invention to provide a product dispenser assembly capable of substituting the complete product space by the pressure space while maintaining a substantially constant driving pressure.
Various prior art documents suggest the use of a reserve gas supply for re-establishing the driving pressure when the driving pressure decreases, thereby preventing or at least delaying a complete depletion of the driving pressure. Some prior art documents suggest the provision of a high pressurized cartridge for supplying gas to the pressure space via a mechanical pressure limiter in case the driving pressure falls below a certain limit, where the limit corresponds to the lowest driving pressure considered to allow a suitable dispensing behaviour. Such technologies have the drawback of being dependent on a mechanical pressure limiter which is expensive and may fail or jam. Failing or jamming pressure limiters may cause an insufficient or an excessive pressure in the pressure space. By having an insufficient pressure in the pressure space the dispensing operations may be discontinued, and by having an excessive pressure in the pressure space a safety hazard may arise due to the risk of explosion of the container. Therefore an intrinsic pressure limitation mechanism is preferred. An example of an intrinsic pressure limiter is presented in US 2006/0049215 where a gas-adsorbing material is used as a reserve gas supply. The gas-adsorbing material may store a large amount of gas within a small volume. The gas is being released from the gas-adsorbing material in response to a driving pressure decrease in the container. The gas-adsorbing material is being wetted with a release-promoting agent for allowing improved release of gas. The gas adsorbing material of the above technology will thus be able to react on and compensate for a pressure decrease in the container by releasing previously stored gas.
In addition to the reduction of the driving pressure caused by the dispensing of the product, leakage of propellant gas and incorrect dispensing operation, which all constitute a permanent loss of driving pressure and has been discussed above, a temporary variation of the driving pressure may be caused by temperature variations in the pressure space of the container. It is well known from the universal gas law that the pressure of a gas depends linearly on the temperature of the gas. Thus, when the pressure space is being subjected to an increased temperature, the driving pressure in the pressure space will be increased as well. The pressure space may be subjected to an increased temperature unintentionally e.g. in case the product container is being stored inside an automobile or similar closed compartment during sunshine. Such temperature effects are well known among users of pressurized containers, and therefore most pressurized containers have labels indicating the maximum storage temperature of the container.
Most containers are pressurized for having a suitable dispensing behaviour around a certain temperature, typically room temperature, i.e. 20° C. In some cases undesired dispensing behaviour may result when a user tries to dispense the product while the container is exposed to a temperature different from room temperature. For example, dispensing from a container which has been stored at a cold temperature, such as 0° C., may result in an insufficient amount of product being dispensed since the driving pressure in the pressure space is lower than it would be at 20° C. Oppositely, when dispensing from a container having a higher temperature than room temperature, such as 50° C., the amount of product being dispensed and the dispensing velocity may be excessive, since the driving pressure in the pressure space is much higher than it would be at room temperature.
In addition to unsuitable dispensing behaviour, high temperatures also constitute a safety risk when handling pressurized containers. Conventional pressurized containers should not be exposed to excessive temperatures since a substantial temperature increase in the pressure space, e.g. by accidental heating, may cause the pressure to increase above the structural pressure limit of the container and the container may consequently rupture or explode. Such ruptures or explosions may cause harm to persons or property located close to the container. Therefore it is a further object of the present invention to provide product dispensing assemblies capable of maintaining or at least substantially maintaining the driving pressure during temperature variations, at least for temperature variations within 3-50° C. and preferably higher temperatures.
Due to the high initial pressures of 6-12 bar used in conventional pressurized containers and the even higher pressures which may occur during accidental heating, the materials used for the container must be substantially rigid for avoiding leakage and ensuring the structural stability of the container even when subjected to high driving pressure forces. Typically metal must be used for the container since plastics and glass are not capable of maintaining the high initial driving pressure, or at least not the occasional higher pressure forces in the pressure space resulting from elevated temperatures. It would therefore be an advantage to be able to use reduced initial pressures, in the range of about 0.1-2 bar and preferably not exceeding 2 bar. Lower initial pressures are preferred since it would allow containers made of other materials than metal, such as plastics. It would further allow thinner containers, more flexible containers and transparent containers. It is therefore yet a further object of the present invention to provide a product dispensing assembly maintaining an initial pressure of no more than 2 bar.